The production of molded articles from resinous fiber materials, for example, airplane fuselage components, is typically subject to various limitations. For instance, it is often more convenient to perform processes on a composite structure after the composite structure has been formed and cured on a bonding fixture and remains affixed thereto, than after removing the composite structure from the bonding fixture. For example, holes must often be drilled within the molded composite structure, wherein the holes are used to align, coordinate, or attach the composite structure to other tools or parts in the manufacturing process. However, current post-cure drill processes are typically limited to drilling holes in or near the part excess while the composite structure remains affixed to the bonding fixture. The part excess comprises the parts of the molded composite structure which are outside the final dimensions of the finished part.
In a typical drilling process, a drill boss is attached to the face of the bonding fixture on which the part is formed in a location in or near the part excess area. A drill bar having a drill bushing installed therein is then mounted on to the drill boss on the tool such that the drill bushing extends over the formed and cured composite structure and establishes the position of the hole to be drilled. A special drill bit with a predetermined length is then inserted through the drill bushing in order to drill the hole. The holes in the part excess generally serve as reference points. Subsequent drilling processes for creating additional engineering coordinating holes in the finished part often requires a complex and expensive secondary drill fixture that indexes from the previously drilled holes which were drilled in the part excess while the post-cure part was still affixed to the bonding fixture.
The current post-cure drill process also has the potential to create a mislocated or out of tolerance hole in certain situations. For instance, during the molding procedure, the composite structure must be sealed to the surface of the bonding fixture with a vacuum bag during the curing process. In order to drill the holes in the finished part, the vacuum bag must ordinarily be removed from the part before the holes are drilled. However, removal of the vacuum bag creates a risk of the part or panel demolding or partially releasing from the bonding fixture. If demolding of the part occurs, the process operator must then reposition the part onto the bonding fixture in a "best fit" position. Since the part has been moved with respect to the bonding fixture, the subsequent drilling process may produce a hole which is misaligned or out of tolerance. Further, where the drill bar is mounted to the drill boss, the drill bar must be flatly seated onto the drill boss and properly aligned prior to the drilling process. If the bar is not positioned correctly onto the boss, an out of tolerance hole will be created. In addition, the length of the bar is typically limited to approximately three to four inches around the part excess in order to produce the required accuracy of the drilled hole. Drill fixtures for extending beyond the part excess and onto the actual part often are complex and costly. Secondary drill fixtures must often be developed which index from a previously drilled hole or set of holes, thereby reducing the accuracy of the location of the final drilled hole.
Another limitation of the current post-cure drill process results from the close proximity of the drill boss attached to the bonding fixture in relation to the part excess. This close proximity often results in resin from the composite molding process migrating around the boss. Thus, subsequent attempts to remove the composite structure and/or the excess resin may possibly cause failure of the weld or solder attaching the boss to the bonding fixture. If the drill boss breaks away from the bonding fixture, the desired hole must be located in the composite structure using a manual layout operation, which also carries a risk of producing a mislocated hole. In addition, a lot of time and labor may be spent in replacing the boss and reworking the bonding fixture.
One approach to resolving the current shortcomings of the existing post-cure drill process involves concerted operator training such that there is awareness of the proper procedures to be followed. However, even proper training and awareness may not serve to resolve the problems of the current process. Thus, there exists a need for a post-cure drill process for a formed composite structure which may be performed with minimal risk of the part or panel demolding or partially releasing from the bonding fixture as the holes are drilled. Further, the apparatus used to perform the procedure should not require assembly or complex alignment prior to drilling the holes. In addition, the apparatus should preferably allow holes to be drilled at any desired position in the composite structure without being limited to close proximity about the part excess. Also, the apparatus should provide that, even in the event of separation from the bonding fixture, that the hole may still be drilled in the composite structure without a complex manual layout operation. Further, it would be desirable for the apparatus to have limited, if any, contact with the resin used to form the composite structure.